1. Field of the Invention
The invention relates to a hand-held power tool which can reduce whirling vibration caused in a tool body or a grip when a tool bit is driven.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2007-237357 discloses a hand-held power tool such as an electric disc grinder having a vibration-proofing structure for reducing transmission of vibration from a tool body in the form of a housing to a grip. In the above-mentioned known vibration-proofing structure, the grip is connected to an axial end of the housing via a spherical structure and an elastic member is disposed between the housing and the grip so that transmission of vibration from the housing to the grip is reduced.
In the electric disc grinder which performs a grinding/polishing operation by rotation of a tool bit in the form of a grinding wheel, when rotating elements (a grinding wheel, a motor, etc.) provided in the electric disc grinder are rotationally driven, if the rotating elements are out of balance with respect to the rotation axis (the center of mass and the center of rotation are misaligned), the rotating elements whirl or rotate on its rotation axis displaced in a direction (radial direction) perpendicular to the rotation axis. Then, the tool body or the grip is caused to perform a swinging movement (circular or elliptic movement) around the center of gravity of the electric disc grinder.
Specifically, the tool body or the grip is caused to swing on the center of gravity of the electric disc grinder, with runout of its long axis in a direction perpendicular to the long axis, so that whirling vibration is caused. Such whirling vibration is constantly caused regardless of the presence or absence of load on the grinding wheel. In the known vibration-proofing structure in which transmission of vibration to the grip is reduced by using the elastic member, however, the above-described whirling vibration cannot be adequately reduced. In this point, further improvement is desired.